Press the record button in the tape transport to start recording. This is the button with the red circle.
Recording always starts from the cursor position in the active window. (This is always shown in the time display in the main control area.) When recording, there will be a count-in, set from the Metronome dialog under the Options menu. The metronome can be on or off and the metronome sound can be controlled using the Metronome dialog. When you record in a track, the recorded data is normally merged with the data currently on the track. This is not the case, however, when punch-in/punch-out is selected (when punch recording). In this case, only the music between the punch points are affected, and the old music is replaced by the new music. (The old music is not merged with the new music.)